While running long distances may not be the best way to lose weight, many runners wonder how many calories they are burning as they pound out those miles. Gretchen Reynolds, our Phys Ed columnist, explains what goes into figuring out your calorie burn:
The answer depends to a significant degree on how large you are. Most studies and online calculators agree that a 150-pound man or woman running at a moderate pace of 10 minutes per mile burns about 115 calories per mile. A runner weighing 200 pounds would burn around 150 calories at the same distance and pace, while a 120-pound sylph would incinerate only about 90 calories.
Physics is inexorable; the more mass you move through space, the more energy you use. However there is good news for intense runners of any size. Recent studies show that strenuous training — meaning the exertion feels like a 7 or 8 on a scale of 1 to 10 — prompts your body to burn more calories than it normally would for at least another 12 hours.
Run Well!
Jen A. Miller
Author, “Running: A Love Story”

Taken from  How Many Calories Do I Burn When Running?